Method for manufacturing permanent magnets



July 26, 1938- Y A. BUcHNR ET AL 2,124,607

METHOD FOR I MANUFACTURING PERMANENT MAGNETS Filed Oct. 17, 1936 2, Sheet-Sheet 1 v Q ,fl I

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METHOD FOR MANUFACTURING PERMANENT MAGNETS" Filed Oct. 17, 1936 2 Sheets-Sheet 2 fyzw vzyw Patented July 26,1938 i 2,124,607

UNITED 'STATES PATENZIY 'oFFlcEf-Iffl DIETHOD FOR MANUFACTURING PERMA- NENT MAGNETS Artur Biichner and Hans Neumann, Berlin-Siemensstadt, and Herman Reinboth,Be1-iin, Germany, assignors to Siemens a Halske Aktiengeselischaft, Sicmensstadt, near Berlin, Germany, a corporation of Germany Application October 1'1, 1936, Serial No. 106,104

- In Germany June 3, 1936 9 Claims. (01. 148-115) Our invention relates to a method for manuadvisable to use a still higher rolling degree parfacturing permanent magnets having a great ticularly above 70%, i. e., to reduce the initial coercive force and a strong remanent magnetism. thickness of the alloy to 30% and less.

Permanent magnets are known which, in ad- T The m o y bestill mp v d y fi in dition to iron and iron-cobalt, contain a great the alloys before cold rolling them. In thisicase 5 amount of aluminum or titanium or of both theseou i ent n pr v d s tw h t tr a m nt on metals. The coercive force and the remanent of which being efiected before and the other after magnetism of these magnets are'higher than the cold rolling the alloys. 1 corresponding properties of the" usual. magnet For the manufacture of permanent magnets 10 steels of martehsitic character. These magnetcopper-nickeleiron alloy'shave proved particularly 1o ieally high-grade alloys are, however, so hard suitable which may contain other metals such as and brittle that it is practically impossible to cobalt or beryllium. P rm' ne t-maen ts ac rdmaohihe them and they must be given their final ns o th inv nt pr s pa a dva form in casting. This renders the manufacture tages when manufactured from ys s s i of certain forms of magnets both difficult and ex- 01' 15 to 40% nickel,- 5 to iron and the re- 15 pensive.- There are also difllculties when the mainder o pp magnets are highly stressed mechanically during The essential improvements as regards e use, for instance, when'they are subjected to conmagnetic prop r obtained according o h tinuous vibrations or stressed by centrifugal invention by co d ng and heat treatin Will forces-as for example in electric machines. appear rom difi r examples r ft 20 Such stresses may lead to the destruction of the s flbedmagnets. The drawings show some graphs illustrating the It has already been proposed to use alloys of P oper es of materials p odu y the method iron, nickel and copper for. making permanent according to the invention. Fig. 1 refers to the magnets. These alloys have the advantage that residual magnetism, Fig. 2 to the magnetic sa't- 25 they can be machined; their magnetic values, liration, and Fig. 3 to the magnetic power of some however, hitherto have been unfavorable. o c o p s oy Figsa 4b illus- An object of my invention is to provide permate the dep y of the magnetic Power on nent magnets which as regards coercive force and the i g degree, and 5 the same magnetic remanent magnetism have substantially similar P p rty in dependency on the iron content in .30

magnetic properties as the known high-grade case of a constant-nickel content. aluminum or titanium steels, and which after More in detail, Figs. l to 3 are graphic reprecasting can be machined by cutting tools, drills sentations of the influence of-the iron content and the like or which can be formed by bending, at a constant nickel content of 20% on the 36 forging or like operations. magnetic properties of the alloy in cast and in A further object of the invention is to improve rolled state.- Bya rolled alloy is understood an I the magnetic properties of the known type of alloy which, after being rolled, is subjected to a permanent magnets containing nickel and copper heat treatment according to the invention. in which the percentage of'iron is lower than the Fig. 1 shows the relation between the residual 40 total percentage of the other constituents. magnetism Biand the .iron content. The full 40 We have found that machineable permanent line represents the alloy treated according to the magnets having particularly favorable magnetic invention, whereas the dash line represents the p p rt es an be pr r alloys containing magnetic properties .of the alloy after casting, 10 o 0% ic 20 to copper and r i. e. before being treated according to the invenof at least another metal of the iron group, espetion. As will be apparent the residual mag-'45 3! iron or iron and cobalt, by firs j ng netlsm of the alloy when roiledis approximately this alloy to a cold rolling process reducing the higher than when only cast. alloy with a rolling degree of over 40%", and by The rolling operation influences also the ratio further subjecting the rolled alloy to a heat treatof the residual. magnetism to the saturation 50 ment which must compriseatleast heating the g g alloy to a temperature above 500 degrees centii grade. The initial thickness of the .body'. pro- 3' duced from the above-mentioned alloy must, in This is shown in Fig. 2 in which the full line and other words. be reduced by the rolling process to the dash line represent the variation of this 5 of the original thickness. In some cases it is ratio for the alloy when coldrolled and when cast ll respectively. As will be seen the residual magnetism of the alloy when cast amounts approximately to 50 to 55% of the saturation, whereas when cold rolled it is increased to about '75 to The coercive force is only slightly affectedby the rolling operation.

Owing to the great increase in the residual magnetism due to the heat treatment also a considerable increase in the magnetic power Brxh'c is obtained as shown in Fig. 3. It is readi-ly apparent that the rolling operation in connection with the annealing treatment influences the magnetic properties of the alloy in'an extremely favorable manner.

A further advantage of the rolled and then annealed material as compared to the same material when only cast, lies in the fact that the demagnetization curves of the rolled samples are more bulged than those of the castsamples. This means that the magnetic power.(BH)mx-has increased to a further amount so that the optimum values lie. 100 to 200% above the maximum values attained with the .cast samples. In,this manner the values of the highly alloyed cobalt steel are approximately attained.

In the above-given explanations, only the max.-

imum values attained with alloys in rolled and non-rolled state have been considered and compared with each other. The influence of the rolling degree and the annealing temperature on Y the material to be treated will now be described.

' more in detail.

Figs. 4a. and 4b are graphic representations of the relation between the magnetic power BrXBHc and the rolling degree. (BI-Is denotes hereinafter the coercive force for the induction B=O, whereas JHc denotes the coercive force for the magnetization J=O. v The difference between BHc and JHc must be considered in the case of alloys having a very great'coercive force, since in these alloys both values may considerably diilfer from one another.) Fig. 4a indicates the values for an'alloy consisting of 57.5% copper,

29% nickel and 22.5% iron which,.after being cold rolled, has been annealed for one hour at a temperature between 600 and 650 degrees centigrade, whereas Fig. 4b represents the values for 'an alloy which has been annealed before and after cold-rolling. The curves shown in each graph were obtained at difierent annealing temperatures. The abscissas of both graphs indicate the rolling degree in percentage.

As will be seen from Fig. 4b thev magnetic power; in the samples annealed-before and after 'the cold rolling operation increases rather uniformly up to a rolling degree. of 65%. The magnetic powerj according to Fig. 4a upon exceeding a a maximum value decreases with a further increasing rolling degree.

Fig. 'is a graphic representation 01 the relation between the magnetic power and the iron content at a constant nickel content of 20%. Here the dash curve represents the magnetic values of the sample when only cast, whereas the dotted line the values for-a material 'whichwas annealed after being rolled. The'fuli line finally shows the magnetic values for a material which has been annealed before and. after rolling the same. From the curves obtainedit be seen that by annealing the material twice the maxi-J mum values for .the magnetic power will be attained. Itisevident that in this casealso the,

residual magnetism and-the coercive force attain their maximum values.. By this annealing treatment the further advantage is obtained that the favorable magnetic values may-still be enhanced by choosing corresponding, if desired different,-

annealing temperatures and periods.

Furthermore, we have found that corresponding improvements may also beattained in other alloys composed essentially .of copper-nickel.

, Thus, for instance, an alloy containing '56 copper, 25% nickel, 18% iron and beryllium if annealed before and after cold rolling has a residual magnetism of 5000 and a coercive force of 350 and, therefore, a magnetic power of 175x10 whereas the corresponding values, if

the alloy is only cast, amount only to 3400, 310 and 10.5)( respectively.

An alloy consisting of 60% copper, 14% iron and 5% cobalt, after being cast, had the following values: Br=3100, sH=400 and 'Br BH=12.4 x 10 which by cold rolling and 'a I following annealing of the alloy increased to 4250,

370 and 153x10 and which by annealing the alloy before and after cold rolling amounted to 3800, 540 and 205x10 a In the case of an admixture of metals which are metallurgicaily similar to cobalt and beryl- 21% nickel,

lium, very high values, particularly as regards the residual magnetismand magnetic power, can

also be attained.

The values of permeability of the material treated according to the invention are different the melting point, quenching the alloys and then cold rolling them. The alloys are preferably I quenched in liquid, such liquids being particularly. favorable which, as oil, havea smaller heat conductivity than water. It is not absolutely necessary that the temperature of the quenching liquid be the .same as the room temperature. In several cases favorable values of magnetic properties have been attained with quenching liquids, the temperature of which lay considerably above the room temperature, for instance,-

with a salt bath, the temperature of which lay. between 150 and 400 degrees centigrade. v

An alloy of 20% nickel, 20% iron and 60% copper was cast into bars of a diameter of '43 mm. The bars were-first rolled to a diameter of 23 mm.

The magnets thus preformed were annealed at a temperature 01,1050 degrees centigrade for ten hours, whereby the materialwas homogenized. After annealing the bars were quenched, then reduced by rollirfg to a diameter of 10.7 mm., annealed at a temperature of 600 degrees centigrade for an hour and finally allowed to cool down in air. The last cooling down of the bars after the annealingtreatment has, no effect on the magnetic properties.

with the magnets thus manufactured the following magnetic values were obtained:

Residual magnetism- B,= 5 280 Induction coercive forces H =453 (for B: 0) Magnetization coercivgforcm ;H,=466 (for I =0) parent that the magnetization curve is strongly bulged so that a very high energy content is obtained in comparison with the coercive force and the residual magnetism.

In addition to the improvement'of the magnetic properties, the invention makes it possible to produce permanent magnets, the wall thickness of which is very small.

As an example, it may be mentioned that the material given in detail in the above-described example was rolled down to a thickness of 0.2 mm. The method was otherwise carried out exactly in the same manner aswith the example dealt with above. The thin and easily flexible platethus produced had the following magnetic values:

Such favorable'results have never been obtained with alloys hitherto known for permanent mageifected and the duration of the heating and the annealing depend upon the thickness of the body to be treated.

When producing alloys containing about 60% copper, about 20% nickel and about 20% iron the coercive force is increased and at the same time the residual magnetism is reduced by lowering the iron content while maintaining the nickel content constant. When the iron content is increased to too great a value both the coercive force and the residual magnetism decrease.

As the examples show the magnetic properties of the magnets made according to the invention are substantially the same as those inherent in magnets made from the known nickel or nickelcobalt steels containing aluminum or titanium. The magnets according to the invention have, however, the advantage that they may easily be machined.

Thepermanent magnets according to the invention are particularly advantageous for electricity meters, moving coil galvanometers, oscillographs, polarized relays,. motors, generators, tachometers, magneto and other inductors, elec-. tromagnetic and electrodynamic telephones, loudspeakers and microphones, magnetic couplings for measuring and .controlling purposes,

- 'rotary magnets for signal transmitters employed in signalling systems etc. The magnetic alloys made according to the invention are particularly advantageous for magnets used connection with revolving parts which are highly stressed, as well as for magnets which owing to the com plicatedform thereof .or to the necessity of drilling and milling operations or the like, are very difficult to be produced by mere casting.

We claim as our invention:

l. The method of manufacturing machineable permanent magnets consisting in annealing an alloy containing about 20% nickel, about 20% iron and about copper to a temperature of about 1,000 degrees centigrade, quenchingsaid 9. In themethod of manufacturing ing degree of over 40% and annealing the same to a temperature between 600 and 650 degrees centigrade.

2. The method of manufacturing machineable permanent magnets, consisting in cold rolling an alloy composed of 20 to 80% copper, 10 to 50% nickel, the remainder consisting of over 5% of at least one metal selected from the group consisting of iron. and cobalt, and of at most 5% other ingredients, with a rolling degree higher than 40%, and heating the rolled alloy to a temperature between 500 and 800 C.

3. The-method of manufacturing permanent magnets, consisting in cold rolling an alloy of 20 to 80% copper, 10 to 50% nickel, the remainder iron and at most 5% of other ingrealloy in liquid, cold rolling the alloy with a rolldients, with a rolling degree of over 70%, and

annealing the rolled alloy to a temperature between 500 and 850 C.

- 4. The method of] manufacturing permanent magnets from. an alloy composed of'l5 to 40% nickel, 5 'to 30% iron, 30- to 80% copper, and fromtraces to 5% of usual additions and impurities, consisting in annealing said alloy to a temperature between 500 and- 700 0., cold rolling said alloy with a rolling degree of over 40%, and annealing the rolled alloy to a temperature between 500 and 700 C. l

5. The method of manufacturing permanent magnets from an alloy composed of 20 to 80% copper, 10 to 50% nickel and the remainder over 5% iron and from traces to 5% additions and impurities, consisting in annealing said alloy at a temperature above 950' C., quenching said alloy, cold rolling said alloy with a rolling degree of over 40%, and finally annealing said rolled alloy to a temperature between 500 and 850 C.

6. The method of manufacturing permanent magnets from an alloy composed .of. 20 to 80% copper, 10 to 50% nickel and a. remainder of over 5% iron and from traces to 5% additions and usual impurities, 'consisting. in annealing said alloy at a temperature between about 1000 C.

,and the melting point, quenching said alloy in liquid, cold rolling the alloy with a rolling degree above 40% and annealing the same to a temperature between 500 and 850 C.

'7. The method of manufacturing permanent magnets composed of more than 20% copper,

10110 50% nickel and more than 5%.of at leastv one metal selected from the group consisting of iron and cobalt, comprising the steps of annealing said alloy at a temperature between about 1000 C. and the melting point, quenching the same, annealing the same to a temperature between 500 and 700 C., cold rolling said alloy with a rolling degree of. over. 40%, and re-annealing said alloy to a temperature between 500 and 700 C.

8. The, method of manufacturing permanent magnets composed. of 20 to 80% copper, 10 to 50% nickel, the remainder containing over 5% of at least one metal selected from the group consisting .of iron andcobalt, and from traces to about:1000 C and the melting point, quenching said magnet in a liquid having a smaller heat conductivity than water, cold rolling said alloy with a rolling degree of over 70%, and annealing the'quenched magnet at a temperature between 500 and 850 C.

permanent magnets from an alloy compoeed of 20 to 80% copper, 15 to 40% nickel, over 5% iron and over 1% cobalt, the steps consisting in annealing said alloy at a temperature between about 1000 C. and the melting point, cold rolling the same with a. rolling degree of. over 40%, and heating the rolled alloy to a tempetatu re between 500 and ARTUR BficnNn HANS NEUMANN.

HERMANN REINBOTH. 

